Fabrication of rhenium



2,149,260 ranmcrmon or Chester T. Sims, Worthington, ohms-a t, by means assignments, to The Batteile Development Corporation, Columbus, Ohio, a corporation of Delaware No Drawing. Application April, 1954,

Serial No. 426,291

1o Claim. (Cl. ass-11.5

work and annealrhenium have failed because the metal United States Patent cracks up early in the cold-working process. Consequently, all previous attempts to provide 'a method for reducing rhenium ingots or bars to sheet or wire form have not been successful and the metal has generally been considered to be incapable of being fabricated on a practical basis.

It is, therefore, an object of this invention to provide a method for fabricating'rhenium metal.

It is another object of this invention to provide a practical method or process for preparing rhenium metal sheet or wrre.

Other objects and advantages of the present invention will be apparent in view of the following detailed description thereof.

In general, this invention comprises a method of fabricating rhenium metal comprising the steps of subiecting the rhenium metal to a number of mild cold-working operations with intermediate annealing steps, then subjecting the metal to more severe cold-working operations with longer time intermediate annealings.

It has now been found that rhenium metal bars and ingots can be reduced to sheet or wire form by a series of cold-working operations with frequent intermediate annealing treatments. *For purposes of illustration, this process will hereinafter be described in terms of specific procedures. However, it will be apparent that the invention is not limited to such specific procedures, but is to be interpreted more broadly'in accordance with the general description above.

Rhenium bars having a square or rectangular cross section may be prepared bypressing, presintering and sinter-' iag rhenium metal powder in accordance with well-known powder metallurgy techniques. It has been found to be desirable andpreferable to first work such bars into a lee Patented June}, 1956 operation to smooth the original faces of the bar should follow. This will produce a negligible reduction in thickness or area. Further cold rolling along the edges of the bar to octagonize the bar is next recommended. Two

or three such operations, with intermediate annealing treatments at 1600-1800 C.-for 20 to 40 minutes, should provide a completely octagonized bar and effect an additional 5-8% reduction in length of the diagonal per cycle. From this point on, reductions of -20%. in cross-sectional area per cold-working operation are pref-- erabk although reductions of a number of cold-swaging Q steps, each producing 10-20% area reduction and with intermediate annealing treatments at 1600-1800 C. for 50-130 minutes may be used. The surfacehardness values should be reduced to less um soo Vickers hardness number by each annealing step. If wire' is to be made from the rhenium bar, cold-drawing operations after a few swaging operations to reduce the area by 10-20% and with intermediate meals for 50-130 minutes at 1600-1800 C. are permissible.

If it is desired to produce rhenium sheet rather than rod or wire, the octagonizlation step, as described above, is not necessary. Instead, a hand-forging or hammering operation is performed along the edges and sides of the bar to be cold rolled to sheet. An annealing treatment at a temperature in the range of from 1600-1800 C. for a period of from -40 minutes should follow the handforging operation. Cold rolling is then performed so as to reduce the thickness of the bar by about 2% per pass, each pass 'being'followed by an annealing treatment at a temperature in the range of from 1600-1800 C. for a period of" from 5-20-40 minutes. These rolling and annealing operations are repeated about five times, so as to obtain a total reduction of the bar of about 10% in thickness. Next, heavier 'cold-rolling passes are employed to reduce the bar to the desired sheet thickness.-

These passes are carried out in such a way as to reduce the bar by about 10% per pass, each pass being followed cold-working operations followed by annealing, followed,

in turn, by more severe cold-working operations such as cold rolling, cold swaging, coldwire-drawing, cold forggenerally octagonal cross-section form, if a final round a period of from 20 to 40 minutes should follow this hand-forging operation. Both steps should be repeated once or twice to effect a total reduction of about 12% on the transverse diagonal of the bar. A cold-rolling ing, cold rod-rolling, cold Turk?s Head rolling, etc., or

any combination of such cold-working processes.

As an example of the operation of the present method, the following data showing the dimensions prior to and following each cold-working and annealing step for the preparation of round rhenium rod are submitted. These data are exemplary only, and not restrictive or definitive of the scope of the process.

Example A rhenium bar, 0.204-inch on a side, having 0.288- inch diagonals, was hand hammered to produce 0.270- inch diagonals (6% -reduction' in diagonal length), then annealed for 30 minutes at 1700 C., band hammered to 0.261-inch diagonals (3% reduction), and annealed again for 30 minutes at 1700 C. This edge-forging operation changed the side dimensions of the bar to 0.205 inch and 0.201 inch, respectively.

The bar was'next 'cold rolled (roll setting 0.195 inch) one pass on each side, producing side dimensions of 0.204 and 0.205 (1% reduction in bar width), respectively.

The forged edges of the bar were then cold rolled to 3 octagonize the rhenium metal bar. The tabulation below indicates the progress of this operation:

Anneal- Rnll Vteken tng Temper- Betttng Hard- Ttme Remarks nes utes) amass Aerceetved.

0.2 0.30-0.24! 460 Reduced 7%. m 1,100

0.215 ans-02st Reduced 5%. 322, l 1,7)-

0. 0.210032 1.-.- Reduced 6%.

calculated to eflect a reduction in cross-sectional area per pass. The alternate swaging and annealing steps were continued until the bar had been reduced to an 0.062-inch diameter wire. The following tabulation shows the step-by-step progress of this process:

Annealing Dis 81:0 Dlame)ter H"lcker-s (m Tlme 'I'em (Minutes) C.)

0. ll, 0. 147 ass 1,100

I 0. m 0.110 642 m 100 1,100

an 00 1,100 0M 0100 U1 2st 00 1,100

0.! 00m 700 210 ll! 1, 100

0.067 0.070 ast ran 1,100

I Bar out into halves.

As has been mentioned previously, rhenium work hardens exceedingly rapidly. In fact, rhenium work hardens to a greater extent than any other metal whose properties are generally known. For this reason, rhenium metal has always developed cracks early in cold-working procedures. -Now, however, a method of fabricating rhenium metal has been providedby this invention. The method requires that the initial cold-working operations be such as to produce only a mild efiect on the metal. In this way, it is believed that the surface grain structureis refined with a consequent increase in strength and without subjecting the underlying metal to great stress. In this manner, a crack-resistant outer skin of refined metal is established so that the tendency of rhenium to edge :rack is overcome. Thus, after a number of cycles of mild cold working and intermediate annealing treatment, the metal is subjected to more severe cold-working operations with longer time intermediate annealings so that the metal is reduced to the desired final fabricated form.

The example above and the'preceding desa'iptive matter show that rheniummetal can be worked and fabricated without destruction of the piece being fabricated, provided the working operations are cold-working operations and are carried out to eflect only mild dimensional changes initially. In addition, frequent intermediate annealing treatments are ;required. By such methods, rhenium metal has been fabricated to form sheets, rods, andwire. Sofarasisnowknowmthisisthefirst method to provide a successful way of fabricating rhenium metal.

A new and useful method of preparing fabricated rhenium metal having been hereinbefore generally and specifically described, it will be apparent that various modifications in the exact procedure may be effected without departing from the scope'of the invention as set forth in the following claims. What is claimed is:

1. A method of fabricating rhenium metal comprising the steps of subjecting the rhenium to a series of coldwork reductions mild enough to effect refinement of only the surface grain structure and thereby provide a crackresistant outer skin of refined. metal, annealing the metal following each such cold-work reduction, and then subjecting the metal to more severe cold-work reductions with intermediate anneals until the desired fabrication is achieved. I 2. The method of claim 1 whereinsaid severe cold-work reductions operate to effect reductions of the order of 5-2096 per operation.

3. The method of claim 1 wherein annealing treatments intermediate the severe cold-work reductions are carried out at a temperature in the range'of from 1600'- 1800' C.

4. The method of claim 1 wherein the severe cold-work reductions effect reductions of the order of 540% per operation and wherein the annealing treatments intermediate said severe reductions are carried out at a temperature in the range of from 1600 -1800 C.

5. A method of fabricating rhenium metal comprising the steps of subjecting the metal to a series of mild coldworking operations 'such as to effect a refinement of only the surface grain structure and thereby provide a crackresistant outer skin, annealing the metal following each such cold-work reduction, then subjecting the metal to a series of severe cold-working operations with intermediate annealing treatments suflicient to reduce the surface hardness of the metal below 350 Vickers hardness number.

6. A method of fabricating rhenium metal comprising the steps of subjecting the 'metal to a series of mild coldworking operations such as to effect a refinement of only the surface grain structure and thereby provide a crackresistant outer skin, annealing the'metal following each such cold-working operation, then subjecting the metal to a second series of cold-working operations wherein reductions of 5-2096 are effected, said cold-working operations being performed alternately with a: sealing treatments sumcient to reduce the surface hardness of the metal below 350 Vickers hardness number.

7. The method of claim 6 wherein the annealing treat ments are performed at a temperature in the range of l600'-l800 C. for a period of time sufficient to produce a surface hardness less than 350 Vickers hardness numher.

8. The method of claim 6 wherein the annealing treatments are performed at a temperature in the range of 1600'l800' C. for a period of from at least 20-40 minutes.

9. The method of claim 6 wherein said second series of cold-working operations efiects reductions of 5 20% in the cross-sectional area of the metal.

10. A method of fabricating rhenium metal comprising the steps of subjecting the rhenium to a series of coldwork reductions mild enough to eflect a refinement of only the surface grain structure and thereby provide a mg each such cold-work red action, subjecting the metal to severe cold-work reductions of the order of 520% per operation, and intermediate these severe cold-work operations annealing the metal at a temperature of 1600- 1800 F. for a period sufficient to reduce the surface 6 hardness of the metal below 350 Vickers hardness numher, and continuing alternate cold-work reduction and annealing .until the desired dimensions are obtained.

References Cited in the file of this patent Materials and Methods," March 1954, pages 88-91. 

1. A METHOD OF FABRICATING RHENIUM METAL COMPRISING THE STEPS OF SUBJECTING THE RHENIUM TO A SERIES OF COLDWORK REDUCTIONS MILD ENOUGH TO EFFECT REFINEMENT OF ONLY THE SURFACE GRAIN STRUCTURE AND THEREBY PROVIDE A CRACKRESISTANT OUTER SKIN OF REFINED METAL, ANNEALING THE METAL FOLLOWING EACH SUCH COLD-WORK REDUCTION, AND THEN SUBJECTING THE METAL TO MORE SEVERE COLD-WORK REDUCTIONS WITH INTERMEDIATE ANNEALS UNTIL THE DESIRED FABRICATION IS ACHIEVED. 